The Benchmark Assessment asked this:

An Upper Merion teacher was once quarantined during a medical procedure, because she was temporarily radioactive. Which accounts for her radioactivity?

• A: She was exposed to intense gamma rays, which made her carbon-12 into radioactive carbon-14.
• B: She ingested radioactive medicine, and radioactive isotopes collected in her thyroid gland.
• C: She received high doses of x-rays, which remained in her body for an extended time.
• D: Wait! Every one of these answers could explain why she was radioactive!

Concisely explain why the right answer was right, and why the wrong answers were wrong.

The Following Answers Were Awarded No Credit. Can you tell why?